How did a 41-year-old American win the world’s toughest bike race?

Virtually no Americans watched the Tour of Spain, a three-week cycling race that ended Sunday in Madrid.

It’s a shame, not only was the racing some of the most memorable in a grand tour that I can recall, but because of the race’s remarkable American winner, Chris Horner. He turns 42 years old next month. After Armstrong was stripped of his Tour de France titles, Horner is the first American grand tour winner since Greg LeMond.

Prior to Horner’s stunning victory, the oldest grand tour winner was Belgian Firmin Lambot, who was 36 when he won the 1922 Tour de France.

Horner is nearly six years older, and won arguably the most demanding grand tour in recent memory. Moreover, average age of pro cyclists at the highest level of the sport is 28. Grand tour cyclists hit their peak, usually, between 27 and 33 years of age.

In winning the tour, Horner climbed better than Vincenzo Nibali, a 28-year-old climber who was probably the best overall rider in the race who earlier this year won the Tour of Italy. Here’s video of the winning move Horner made on the diabolical final climb of Stage 20.

Horner sits on the ground, flanked by members of his team, after the 20th stage. (AFP PHOTO)

So how did Chris Horner, who had never previously finished in the top five of a grand tour, do it?

Like every cyclist of this era, he has faced serious questions about doping, the using a performance enhancing drugs. This is only natural following the Lance Armstrong era, especially for a rider who rides on the team Armstrong formed during his comeback.

Full disclosure: I’d love for Horner to be clean. He seems like a genuinely good guy, and he’s had a lot of bad luck in his career before finally finding some success. The cynic in me is doubtful, however, especially as it remains possible to dope one’s blood in cycling despite it possessing the most sophisticated drug testing policy in any sport.

Horner, a few minutes later, having recovered a bit from his Stage 20 effort. (AFP Photo)

What I’m not sure of is how significant a decline there is physically, in an endurance athlete, between the age of 30 and 40. So I rang up Dr. Theodore Shybut, a sports medicine expert at the Baylor College of Medicine.

Both an athlete’s endurance and power output fall off by the late 30s, Shybut said.

With regard to endurance, the fall-off generally begins in the mid-30s. At this time a person’s ability to sustain a high level of activity — say running fast, but not sprinting — without burning up all of one’s energy begins to diminish. This is known as the anaerobic threshold. By the mid-30s this threshold tends to lower a bit in a typical athlete, Shybut said. This means Horner, at the same energy expenditure has he used five to seven years ago, would be going slower to today.

“This is one reason why, in general, we don’t see a lot of Olympic athletes in strength and endurance events in their late 30s and 40s,” Shybut said.

Torres in 2008.

Another critical factor is that athletes lose some of their ability to recover after hard efforts by their mid- to late-30s. A grand tour encompasses 21 stages of racing with just two rest days during the event. Day-to-day recovery is essential.

With power output the drop-off typically comes even earlier. For cyclists, a critical ability is their maximum capacity to transport and use oxygen, or their VO2 max.

“This does tend to decrease as well, in general for peak performance in power sports like sprinting, that peak comes in the late 20s,” Shybut said.

So for a cyclist like Horner, who puts out a maximum effort for 15 to 20 minutes on a very hard climb, his peak power would probably have come in his late 20s.

All of this looks pretty bad for Horner. However, Shybut noted, there are a handful of older athletes who have achieved peak status late in life. Notably U.S. swimmer Dara Torres, at the age of 41, won three silver medals at the 2008 Olympics and set an American record in the 50-meter freestyle.

It is theoretically possible that some athletes could maintain or even reach their physiological peak in their late 30s, Shybut said. The only way to definitively prove this would be to perform exercise and blood tests in ones 20s, 30s and 40s, and measure the changes. Unfortunately this information isn’t available for Horner as it could, in some way, exonerate him from doping allegations were he able to show improvement these physiological metrics.

Horner, in other words, might have great genes. But the genetics of endurance sports is not to the point yet where we know the genetic markers for 40-year-old super athletes. So a DNA test can’t validate Horner either, at least not yet.

Regardless, as someone who recently turned 40, I tip my cap at a fellow 40-something taking it to the kids, many of whom were also quite probably doping to some extent.